Fixed disk drives are data storage devices in which a data transducer head "flies" in very close proximity, e.g. 4-8 microinches, above a rotating data storage surface. Because of the minute clearance between the head and the rotating disk, it is necessary to "fly" the head in a very controlled, hermetically sealed environment.
In order to establish the requisite environment as free from particulate contamination, head and disk assemblies typically include bases and removable covers mounted onto the base. The covers are removable to enable factory servicing of the head and disk assembly in low-particulate "clean room" or "clean tunnel" environments. In order to maintain the requisite hermetic seal against environmental contamination, usually a sealing gasket of suitable elastomeric material, is compressed between the cover and the base of the head and disk assembly. While the seal is very effective in preventing intrusion of contaminating particulates into the interior space of the head and disk assembly, it may also permit electromagnetic pollution to enter and corrupt the data storage and retrieval function of the disk drive data storage device, particularly where the device is located in close proximity to other electronic circuit elements, such as switching power supplies, high speed microprocessors, etc., which generate RFI/EMI.
In some head and disk assemblies, the base is cast of metal, such as aluminum alloy, and the cover is a sheet metal cutout or stamping, with very little function other than to enclose the open end of the base casting. In other head and disk assemblies, the cover, while remaining a cutout or stamping, also functions to mount or help secure components. In some examples found in the prior art, the journal assembly of a mass balanced rotary voice coil head positioner actuator is secured between a floor of the base casting and the cover, thereby to achieve greater rigidity and resistance to vibration by the actuator.
Disk drives have become smaller. Today, disk drives having two and one half inch diameter storage disks have been realized. These sub-micro Winchester disk drive subsystems are finding acceptance and application within miniaturized computing systems, such as laptop computers and electronic notepads. In these highly compacted devices (e.g. single disk versions may have a height including circuit board of 5/8 inch, a width of 23/4 inches, and a length of 33/4 inches, for example), the head and disk assembly of the disk drive is frequently mounted directly to a "motherboard" of the device, in very close proximity to sources of electromagnetic or radio frequency interference, of the types noted above. The most common susceptibility to RFI/EMI is through a peripheral gap that exists between the base and cover, a gap heretofore conventionally filled with an elastomeric sealing gasket.
A number of approaches have been taken in an attempt to seal the base-cover gap against RFI/EMI. One approach has been to apply a strip of copper, or conductive braid, over the gap between the base and the cover. Another approach has been to employ a conductive, typically carbon-loaded elastomeric gasket between the base and cover. Neither of these approaches has proven to be entirely satisfactory, particularly where the head and disk assembly must be in close proximity to RFI/EMI sources within a compact computing system or environment.